The purpose of this study is to compare a dopamine agonist pramipexole with carbidopa-levodopa in the initial treatment of early, symptomatic Parkinson's disease. Parkinson's disease is a very difficult to treat neurodegenerative syndrome and carbidopa-levodopa, a mainstay of treatment, is associated with adverse neurologic reactions. This is a multi-center, randomized, double-blind, parellel, placebo-controlled trial of a total of 300 patients to compare the 2 therapies. The primary outcome measure is the time until the first dopaminergic motor complication, and secondary measures include quality of life and the requirement for supplemental study drug and additional carbidopa-levodopa. Recruitment is completed. Data analysis is not completed in this multi-center clinical trial. The protocol is amended to allow those subjects participating in the accompanying SPECT Imaging study M/2730/0096 to have the final imaging procedure accomplished prior to the study drug being discontinued at the termination of the trial. The final thyroid function tests are eliminated as this information is no longer used prior to performing SPECT imaging scans.